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Axford Lecture

NASA Goddard Space Flight Center

Mon- 29 Jul, 4:15-4:45pm
Nicoll Room, Level 3

"Magnetic Fields of the Gas Giants Jupiter and Saturn"

Gas giants Jupiter and Saturn have been objects of intensive study for decades, with in-situ observations first gathered by the Pioneer and Voyager flybys in the past century. From these missions we learned that the gas giants are at best fraternal twins, birthed in the solar nebula and largely of solar composition, but with dramatically different personalities. Saturn, with its uniquely axisymmetric magnetic field arising from differential rotation of its deep atmosphere, is resplendent with its brilliant ring system, enduring in its present form for tens, or perhaps hundreds, of million years. The more massive, and likely first-born twin, Jupiter, hosts a complex and non-axisymmetric magnetic field that long ago reduced his rings to the residue that remains today. Both twins, recently visited again (Cassini at Saturn; Juno at Jupiter), have already surrendered many secrets to these polar-orbiting observatories, reaching beneath the clouds with measurements of gravity and magnetic fields, and microwave emissions (Juno). The axisymmetry of Saturn’s zonal harmonic magnetic field was tested anew, and found not wanting. Sliding between Saturn’s rings and atmosphere, Cassini found the rings shedding mass via orbital decay and via electromagnetic erosion of the rings (“ring rain”), delivering mass along magnetic field lines to the atmosphere. Jupiter’s magnetic field, still being mapped, was found to be surprisingly complex, with a non-dipolar magnetic field in its northern hemisphere, and a dipolar magnetic field south of the equator, where an enigmatic “Great Blue Spot” resides within a band of opposite polarity. Jupiter’s magnetic field is likely sculpted by differential rotation of its belts and zones, extending to depths (few thousand km) where the electrical conductivity of its molecular hydrogen atmosphere grips field lines. In this lecture, I hope to grip you with some of the fascinating insights delivered by Cassini and Juno, and perhaps entertain you with historical and artistic perspective.

Since joining NASA’s Goddard Space Flight Center in 1979, Jack Connerney has participated in magnetic field investigations of every magnetized planet in the solar system, from Mercury, Earth and Mars to Jupiter, Saturn, Uranus, and Neptune. He developed novel techniques for measurement, analysis, and modeling of planetary magnetic fields using both in-situ and remote observations. His >200 scientific publications span several disciplines, including planetary magnetic fields, crustal magnetism, geophysical inverse theory, ionospheres, aurorae, and the electrodynamic interaction of satellites and ring systems with a planetary magnetic field. He was Co-Investigator on the Voyager 1&2, Tethered Satellite, Mars Observer and Mars Global Surveyor magnetic field investigations, eventually assuming leadership of the magnetometer group at GSFC. Now with the Space Research Corporation (at GSFC), Jack continues as Deputy Principal Investigator for Juno, the New Frontier Mission to Jupiter and leads the magnetic field investigations on Juno and MAVEN (in Mars orbit).

Dr. Connerney received a B.S. (1972) and Ph.D. (1979) in Engineering Physics at Cornell University and began his Goddard career as a NAS/NRC postdoctoral fellow, accumulating 35+ years of experience in space systems, space flight hardware, and planetary research. He is a fellow of the American Geophysical Union (2009), recipient of the NASA Medal for Exceptional Science Achievement (1986), the John C. Lindsay Memorial Award for Space Science (1994), the NASA Medal for Exceptional Achievement (1998), and the Doctor Technices Honoris Causa from the Technical University of Denmark (2015).